This invention generally relates to medical devices, and particularly to intracorporeal devices for therapeutic or diagnostic uses such as balloon catheters, stent covers, and vascular grafts.
In percutaneous transluminal coronary angioplasty (PTCA) procedures, a guiding catheter is advanced until the distal tip of the guiding catheter is seated in the ostium of a desired coronary artery. A guidewire, positioned within an inner lumen of a dilatation catheter, is first advanced out of the distal end of the guiding catheter into the patient's coronary artery until the distal end of the guidewire crosses a lesion to be dilated. Then the dilatation catheter having an inflatable balloon on the distal portion thereof is advanced into the patient's coronary anatomy, over the previously introduced guidewire, until the balloon of the dilatation catheter is properly positioned across the lesion. Once properly positioned, the dilatation balloon is inflated with fluid one or more times to a predetermined size at relatively high pressures (e.g. greater than 8 atmospheres) so that the stenosis is compressed against the arterial wall and the wall expanded to open up the passageway. Generally, the inflated diameter of the balloon is approximately the same diameter as the native diameter of the body lumen being dilated so as to complete the dilatation but not overexpand the artery wall. Substantial, uncontrolled expansion of the balloon against the vessel wall can cause trauma to the vessel wall. After the balloon is finally deflated, blood flow resumes through the dilated artery and the dilatation catheter can be removed therefrom.
In the design of expandable medical device components such as catheter balloons, the compliance of the component is an important consideration. Compliance is a measure of the extent of expansion in response to an increase in inflation pressure. Catheter balloons are typically classified as noncompliant, semi-compliant, and compliant, depending on the amount of radial expansion over a given inflation pressure range. Poly(ethylene terephthalate) (PET) is a conventional balloon material generally considered to have noncompliant or low compliant expansion, whereas materials such as polyethylene are typically considered to have compliant expansion. For many applications, intravascular catheter balloons should be formed from relatively strong materials in order to withstand the pressures necessary for various procedures without failing. Typically, this requires the use of a material that does not stretch appreciably, and which consequently necessitates that the deflated balloon material be folded around the catheter shaft in the form of wings, prior to inflation. However, it can be desirable to employ balloons, referred to as formed-in-place balloons, that are not folded prior to inflation, but which are instead expanded to the working diameter from a generally cylindrical or tubular shape (i.e., essentially no wings) having a nominal diameter that conforms to the catheter shaft.
In angioplasty procedures, there may be restenosis of the artery, i.e. reformation of the arterial blockage, which necessitates either another angioplasty procedure, or some other method of repairing or strengthening the dilated area. To reduce the restenosis rate and to strengthen the dilated area, physicians frequently implant a stent inside the artery at the site of the lesion. Stents may also be used to repair vessels having an intimal flap or dissection or to generally strengthen a weakened section of a vessel. Stents are usually delivered to a desired location within a coronary artery in a contracted condition on a balloon of a catheter which is similar in many respects to a balloon angioplasty catheter, and expanded to a larger diameter by expansion of the balloon. The balloon is deflated to remove the catheter and the stent left in place within the artery at the site of the dilated lesion. Stent covers on an inner or an outer surface of the stent have been used in, for example, the treatment of pseudo-aneurysms and perforated arteries, and to prevent prolapse of plaque. Similarly, vascular grafts comprising cylindrical tubes made from tissue or synthetic materials such as DACRON, may be implanted in vessels to strengthen or repair the vessel, or used in an anastomosis procedure to connect vessels segments together.
It would be a significant advance to provide a catheter balloon or other expandable medical device component with improved flexibility, strength and compliance characteristics.